The research found that by examining both the nervous system and the heart’s electrical system, cardiologists could better identify which patients were at highest risk of cardiac arrest or death, even years after a heart attack. “This is important because past studies, focusing on a single test, failed to identify most people at risk,” said Derek V. Exner, M.D., M.P.H., heart rhythm specialist at the University of Calgary’s Libin Cardiovascular Institute of Alberta, in Canada. “We developed a simple method of identifying approximately twice as many people at risk. That means we can potentially save more lives.”

For the study, Exner and his colleagues enrolled 322 patients who had suffered a heart attack and had at least a mild abnormality in the heart’s pumping ability. Within 2 to 4 weeks of the heart attack, and again at 10 to 14 weeks, they performed a variety of tests to measure the status of both the nervous system and the heart’s electrical system. They then tracked patients for an average of nearly four years. The researchers analysed the heart’s electrical system by looking for T-wave alternans (TWA) and the electrocardiogram for evidence that the nervous system was on high alert by looking for abnormalities in “heart rate turbulence” (HRT).

Early after a heart attack, TWA and impaired HRT were not accurate warning signs of future risk. At the 10- to 14-week mark, however, TWA and impaired HRT clearly identified patients at increased risk - and they were particularly powerful when used in combination. The 20 percent of patients who had both TWA and impaired HRT on the all-day heart monitor and, in addition, had a persistent abnormality in the heart’s pumping ability, faced more than six times the risk of cardiac arrest or death during follow-up when compared to other patients in the study.